An optical time-domain reflectometer (“OTDR”) is an opto-electronic instrument used to characterize an optical fiber. A typical OTDR injects a series of optical pulses into the fiber during a testing process. From the same end of the fiber, the OTDR also extracts light that is scattered and reflected back from points in the fiber due to irregularities in the optical fiber structure. This process is equivalent to the manner in which an electronic time-domain reflectometer may measure reflections caused by changes in the impedance of the cable under test. Accordingly, the strength of the back-reflected light is measured and integrated as a function of time, and is plotted as a function of fiber length.
OTDRs have conventionally been standard equipment for the characterization of optical fiber. Specifically, it is well known that by transmitting a pulse down a fiber and analyzing the back-reflected light, the loss of the fiber may then be characterized. OTDRs may characterize the loss and length of an examined fiber during manufacture, during warehousing, during installation, and during splicing. OTDRs are also used in measuring optical return loss in the fiber, as well as locating faults in the fiber, such as breaks. Faults or failures in the fiber may be costly, in terms of repairing the fiber, as well as any adverse affects in service (e.g., disruption or loss of service). However, conventional identification and verification of specific fibers within a network are prone to human error.
Optical frequency domain reflectometers are designed to have better spatial resolution than a traditional OTDR, and thus can make hi-resolution measurements of the backscattered light of an optical fiber. However, OFDR's typically have a shorter measurement range. They were initially designed to characterize small optical devices, rather than long optical fibers used for transmission of signals. By employing interferometric technqiues, they are capable of a spatial resolution as small as 20 microns. However, their operating range is generally limited to making measurements over distances less than 100 m.